1. Field of the Invention
The present invention relates to a method of manufacturing slide fasteners from a pair of slide fastener stringers of continuous or substantially endless length.
2. Prior Art
Various attempts have been made to remove helically coiled or meandering type fastener elements which are sewn to a pair of continuous slide fastener stringers, thereby providing element-free gaps in the slide fastener chain. To accomplish such element removal, it is known to cut off coupling heads of the fastener elements to be taken out, and then to pull out their leg portions from the sewing threads, so as to allow the sewing threads to remain unbroken, holding adjacent fastener elements stably against sticking up or separation from the stringer tapes. This attempt, however, must be performed by relatively complicated apparatus.
According to another effort, a film of thermoplastic synthetic resin is bonded to a pair of slide fastener stringers so as to extend across and over the slide fastener chain. The bonded film is then cut to provide an element-free space therein, so that the cut edge can be prevented from fraying during handling and use. With this process, the step of applying a film is necessary independently of the space cutting step, and the film residual on the stringers tends to obstract the passage therethrough of a sewing needle when the slide fastener is to be sewn onto a garment.
To find a way out of these problems, a fabric formed of thermoplastic synthetic fibers or their blended yarn has been proposed for use as slide fastener stringer tapes. A group of fastener elements corresponding to a desired length are first cut away from such stringer tapes with the sewing threads being left on the tape. A portion of the tapes which has an element-free edge is then cut out to provide a space therein. Simultaneously with the space formation, the cut edge of the tapes is heat-treated such as by a high-frequency welder, so as to be fraying-free. This arrangement, however, also involves two space-forming steps to work with, thus adversely affecting the rate of production. Further, the element-free edges of the tapes have loose sewing threads that permit adjacent fastener elements to come off and act as a barrier when attaching a slider onto the slide fastener chain.